Recently, with widespread use of the Internet, a significant amount of content is made available to the public by web servers. In addition, web pages increasingly contain real time data, such as weather forecast data and stock price data. Such real time data is often useless unless the data is new. However, in many cases, it is difficult to retrieve new content from a significant amount of content. Conventionally, retrieval techniques, such as search engines, are used to retrieve the new content. Search engines can retrieve only web pages containing a keyword specified by users. Furthermore, a plurality of retrieved web pages is sorted by the last update date or the reference frequency, which can allow users to find a desired page more easily.
On the other hand, techniques allowing easier retrieval of information from web pages by functions provided in web browsers have been suggested. In Japanese Unexamined Patent Application Publication No. 10-222415 (“Yukihiko”), a browser displays a plurality of cross-linked web pages as data of a tree structure having a plurality of nodes. The browser displays a node for web pages that have been updated after a specific date more distinctly than the other node. Additionally, in Japanese Unexamined Patent Application Publication No. 2003-345826 (“Susumu”), a browser displays a list of contents in a web page in association with update date of the contents. According to these techniques, users can recognize an update history of the contents.
In search engines, web pages are employed as the unit of retrieval. For this reason, recently-updated web pages may be retrieved preferentially even if old content is included therein. In such a case, it is difficult to distinguish useful information from useless information in the web page. In addition, web pages that are frequently referred to may be retrieved and displayed preferentially even if the web pages have not been updated for a while. In this case, it becomes more difficult to retrieve new information.
Furthermore, in a technique described in Yukihiko, information is displayed in a tree structure that schematically showing a plurality of web pages, whereas, in a technique described in Susumu, a list of a plurality of web pages is displayed. Such a displaying fashion significantly differs from that of web pages displayed by general web browsers. Because of this, although this displaying fashion may be convenient for creation/management of web pages, the displaying fashion is unsuitable for enabling users to intuitively recognize whether or not each of contents contained in the web page is new. Moreover, depending on types of content, there is a case where content is useful even if the content is old. It is impossible to distinguish such useful content from old useless content.